[GitHub] pnowojski commented on a change in pull request #6417: [FLINK-9913][runtime] Improve output serialization only once in RecordWriter

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pnowojski commented on a change in pull request #6417: [FLINK-9913][runtime] Improve output serialization only once in RecordWriter
URL: https://github.com/apache/flink/pull/6417#discussion_r215611369
 
 

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 File path: flink-runtime/src/main/java/org/apache/flink/runtime/io/network/api/writer/RecordWriter.java
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 @@ -197,40 +214,39 @@ public void setMetricGroup(TaskIOMetricGroup metrics) {
 	 * Marks the current {@link BufferBuilder} as finished and clears the state for next one.
 	 */
 	private void tryFinishCurrentBufferBuilder(int targetChannel) {
-		if (bufferBuilders[targetChannel].isPresent()) {
-			BufferBuilder bufferBuilder = bufferBuilders[targetChannel].get();
+		Optional<BufferBuilder> bufferBuilderOpt = bufferBuilders[targetChannel];
 
 Review comment:
   Rename to `bufferBuilder` (marking type in variable name is not the best practice). 
   
   Have you seen throughput improvements by introducing this local variable? If not, maybe revert the change?
   
   FYI: When I was writing this code, I didn't see any performance improvement (and I was testing this exact change). Removing one extra CPU cache read (second `bufferBuilders[targetChannel]` access will either be optimised out or it will be a read from CPU caches/registries) usually hardly matters compared to taking locks :( 

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